Especially in pressurised cabins of commercial aircraft and transport aircraft, the humidity of the air can drop during flight. For example the humidity of the air can drop to as little as 3% relative humidity (% RH) at room temperature. Passengers may consider such low humidity uncomfortable.
In order to increase thermal comfort, the cabin air can be humidified in part or in whole. U.S. Pat. No. 5,359,692 describes a system which uses electrical energy for evaporating water. U.S. Pat. No. 4,272,014 and EP 0 031701 describe systems which use hot air to evaporate water. In these systems the water vapour is mixed with the cooled air and is supplied to the air conditioning unit. These systems are associated with a disadvantage in that the thermal load in the cabin is increased by mixing water vapour with hot air.
Furthermore, there are air humidifiers which are based on the principle of cold evaporation, such as for example the diaphragm humidifier described in U.S. Pat. No. 5,595,690. EP 0 779 207 B1 describes an atomiser and an evaporator with a porous dripper bed.
In particular in aircraft engineering, individual components have to be highly reliable.